Problem: If $a + b = 5$ and $x + y + z = 5$, what is $4x + 4y + 4z - 2b - 2a$ ?
Solution: $= -2a - 2b + 4x + 4y + 4z$ $= (-2) \cdot (a + b) + (4) \cdot (x + y + z)$ $= (-2) \cdot (5) + (4) \cdot (5)$ $= -10 + 20$ $= 10$